Analysis of the complex deoxidation of carbon steel melts

The joint complex deoxidation of carbon steel melts is analyzed. A procedure is proposed to calculate the equilibrium oxygen concentration in a melt. Rail steel is used as an example to study the joint complex deoxidation of a melt by aluminum and silicon. Mullite (2Al₂O₃ · 3SiO₂) and kyanite (Al₂O₃ · SiO₂) are considered as the reaction products. Thermodynamic calculations demonstrate that the deoxidizing capacity of aluminum is increased in the presence of silicon in a melt. In this case, a substantial increase in the deoxidizing capacity in the concentration range 0.001–0.1 wt % Al is achieved when kyanite (Al₂O₃ · SiO₂) forms in the reaction products. The results of laboratory and industrial experiments on complex deoxidation are shown to agree well with the calculated data. These results demonstrate that the proposed calculation procedure can be recommended to determine the equilibrium oxygen concentration in a melt in the presence of several deoxidizing elements.     

钢中铝-硅-锰复合脱氧反应的热力学计算

复合脱氧后钢液的最终氧含量优于单独脱氧的效果,同时复合脱氧可产生低熔点、易聚合长大的复合夹杂物,实现最佳的脱氧效果。用热力学方法计算了铝-硅-锰复合脱氧的效果,结果表明,在不同硅锰比下,复合脱氧均比单独用铝脱氧的最终氧含量要低;根据脱氧产物为锰铝榴石的原则得出了合金脱氧剂的组成成分。热态试验验证了理论计算结果。     

Thermodynamic Analysis of Deoxidation of Titanium Through the Formation of Rare-Earth Oxyfluorides

In this work, the possibility of the direct removal of oxygen species from metallic Ti through the formation of rare-earth oxyfluorides has been investigated from a thermodynamic viewpoint. The deoxidation limit of β-Ti using rare-earth metals (M: Y, La, Ce, and Nd) as deoxidants was evaluated. It was found that Ti metal with an oxygen concentration of 200 mass ppm or less could be theoretically obtained under the M/MOF/MF₃ equilibrium at 1300 K (1027 °C), which suggested a possibility of reducing the oxygen content in Ti below 500 mass ppm utilizing a fluoride-based molten salt. Furthermore, a new deoxidation process, in which oxygen was removed in the form of MOF compounds using Mg deoxidant, was discussed as well. The obtained results revealed that the oxygen content in β-Ti could be theoretically reduced to a level below 1000 mass ppm using a MF₃-containing molten salt equilibrated with Mg. Rare-earth metals and their alloys are usually produced by the electrolysis in a fluoride-based molten salt; hence, the modern industrial electrolysis techniques can be potentially utilized for deoxidizing Ti scrap.     

Optimization of Intensified Silicon Deoxidation

For demanding wire applications steel cleanliness should be very high and the inclusions inevitably found in steel should be harmless. This means strict control of inclusions' size, quantity, and composition, pursuing deformable inclusions in rolling conditions. Primary inclusions are formed during steel treatment in the ladle. Most of these are removed to the ladle slag or on the lining. However, the rest of the inclusions still remain through the successive process stages, and some new inclusions are formed during casting and solidification. Conventionally, deformable inclusions are produced by Si–Mn deoxidation resulting in MnO–SiO₂–Al₂O₃ inclusions. This leaves, however, the oxygen content too high for demanding applications. In order to get really clean steel, the Si deoxidation needs to be strengthened by lowering the activity of SiO₂ forming in steel. This can be done by bringing the steel in intimate contact with a slag containing SiO₂–MnO–Al₂O₃ and additionally CaO and some MgO. With this kind of intensified Si deoxidation it is possible to produce steels with low oxygen content having inclusions that will elongate at rolling. In this paper thermodynamic examination of potential slag systems and compositions to equilibrate with steels having medium carbon and high silicon were scrutinized. The optimal slag composition for producing low‐O steels with deformable inclusions was evaluated by using FactSage thermodynamic calculation program. The lowest SiO₂ activities at the region in which slag is still liquid at 1400°C, can be found when slag composition is approximately 36–40 wt% SiO_2, 6–18 wt% Al₂O_3, 30–40 wt% CaO, 6–8 wt% MgO, and 2–4 wt% MnO. Industrial heats using intensified Si deoxidation and slag based inclusion engineering were produced in a steel mill with 60 tons heat size. Inclusions and slag compositions were in satisfactory accordance with the theoretical examinations, though some scattering was discovered.     

Model of Desulphurization of Steel Melts in Ladles – Deoxidation and Slag Formers Calculation

The authors present their own model applicable for effective desulphurization of steel by ladle treatment. The model is based on a thermodynamic approach (equilibrium data) and technological data (correction factors). It consists of two parts. In the first part the authors present the formulae derived for estimation of the additions of deoxidation agents which ensure sufficiently low oxygen level prior to the desulphurization process, while the other part gives a qualitative and quantitative selection of slag formers to achieve low final levels of sulphur in steel. For the deoxidation process two variants were considered: (i) with Al only (for low silicon steels) or (ii) Al‐Si (for silicon steels) as deoxidizers. For the desulphurization process three variants were assumed as to ladle slag composition: (i) slag consisting of a fraction of furnace slag, lime addition and deoxidation products, (ii) slag made of synthetic CaO–Al₂O₃ and (iii) slag based on lime and fluorspar. The model formulae for desulphurization were derived using the sulphide capacity concept which relies on the optical basicity. In addition, rough estimates of the slag liquidus temperatures are given. A numeric example of the model application and the model algorithm (appendix) are enclosed.     

Thermodynamic assessment of Mg deoxidation reaction of liquid iron and equilibria of [Mg]‐[Al]‐[O] and [Mg]‐[S]‐[O]

The deoxidation reaction of magnesium was investigated thermodynamically employing the equilibrium system between magnesium vapour and liquid iron in the molybdenum chamber sealed with an iron cover at 1873 K as a fundamental study to address the clean steel production technology in the steelmaking process. The previously reported thermodynamic data for magnesium deoxidation reaction are limitedly in good agreement with only their respective specific Mg concentration range, but fail to explain the thermodynamic equilibria generally over the wider range of magnesium concentration beyond the limited range. Therefore, the equilibrium constant, K_Mg for the magnesium deoxidation reaction as well as the first and second‐order interaction parameters between magnesium and oxygen were determined over the extensive magnesium mass content range covering up to 0.04 %. Furthermore, the phase stability diagram based on the equilibria of [Mg]‐[Al]‐[O] in liquid iron for the purpose of controlling the oxide inclusions in the steelmaking process was accomplished using the determined thermodynamic parameters. The equilibria of [Mg]‐[S]‐[O] were also discussed in order to evaluate the utilisation of Mg as a desulphurizing agent as well as deoxidizer in the production process of low carbon steels.     

VOD吹炼不锈钢脱氧工艺及渣系分析

对长钢目前VOD吹炼不锈钢所用脱氧刺、渣系进行了分析，论述了脱氧刺中Al／Si比值、Ca的百分含量及脱氧剂加入顺序对不锈钢氧含量的影响，并讨论了VOD精炼渣组份、碱度及渣氧化性与钢中氧含量的关系．通过这些论述，提出了降低VOD吹炼不锈钢氧含量的工艺措施。     

Inclusion control of ferritic stainless steel by aluminum deoxidation and calcium treatment

A thermodynamic equilibrium between aluminum and oxygen and inclusion morphology in the Fe-16Cr stainless steel were investigated to understand the fundamentals of the aluminum deoxidation technology for ferritic stainless steels. Further, the effect of calcium addition on the changes in chemistry and morphology of inclusions was discussed. The measured results for the aluminum-oxygen equilibria exhibit relatively good agreement with the calculated values, indicating that an introduction of the first-and second-order interaction parameters, recently reported, is reasonable to numerically express the aluminum deoxidation equilibrium in a ferritic stainless steel. In the composition of dissolved aluminum content greater than about 60 ppm, pure alumina particles were observed, while the alumino-manganese silicates containing Cr₂O₃ appeared at less than 20 mass ppm of dissolved aluminum. The formation of calcium aluminate inclusions after Ca treatment can be discussed based on the thermodynamic equilibria among calcium, aluminum, and oxygen in the steel melt. In the composition of steel melt with relatively high content of calcium and low aluminum, the log ( ) of inclusions linearly increases by increasing the log [a _Ca/a _Al ² ·a _O ² ] with the slope close to unity. However, the slope of the line is significantly lower than the expected value in the composition of steel melt with relatively low calcium and high aluminum contents.     

钛稳定超纯铁素体不锈钢硅铝复合脱氧的试验研究

 为改进超纯铁素体不锈钢的脱氧工艺,提高夹杂物控制水平,在硅钼高温电阻炉内对钛稳定超纯铁素体不锈钢的精炼过程进行了试验研究。结合热力学计算,研究了不同Si、Al含量(质量分数,下同)比值的硅铝合金的脱氧效果,以及脱氧、钛合金化和钙处理后钢中典型夹杂物的组成和形貌及粒度分布。结果表明：钢中初始氧含量相近的条件下,硅铝合金复合脱氧的钢中酸溶铝、全氧量与纯铝脱氧结果相近。硅铝复合脱氧后钢中夹杂物主要为(MgO-)Al2O3-SiO2复合脱氧产物。钛合金化后夹杂物的类型主要为Al2O3-MgO-(SiO2)-TiOx复合夹杂物和TiN。钙处理后的夹杂物主要为球形的MgO-Al2O3-CaO-SiO2-TiOx类复合氧化物。采用硅铝合金复合脱氧比纯铝脱氧钢的夹杂物的总数量、总面积和平均粒径均要小。     

AWCF脱氧研究

本文提出了将ＣａＣＯ＿３渣剂与铝结合（ＡＷＣＦ）进行钢水脱氧的设想，并且进行了试验，结果表明，此方法可使脱氧速度加快，钢中氧含量更低。另外还做了简要的分析。     

铁液中Al-C复合脱氧热力学

利用热力学方法,针对铁液中铁水深脱硫条件所需要的低氧含量,研究了Al-C-O平衡时铁溶液中氧含量的变化规律.通过对C、Al及Al-C复合脱氧反应脱氧常数的比较得出,在1573K温度下,铁液中用Al-C复合脱氧,其脱氧能力比单独使用C脱氧能力强.用热力学理论得出1573K温度下铁液中用Al-C复合脱氧的平衡曲线.研究表明:在温度一定时,随着C的活度a_C的增大,Al-C复合脱氧能力逐渐增强;在a_C一定的情况下,随着温度的升高,Al-C复合脱氧能力逐渐减弱.      

特殊钢精炼中的脱氧及夹杂物控制

 特殊钢是针对客户提出的质量要求,钢厂不断改进工艺,逐步提高成分、尺寸精确度和洁净度的各类钢的总称。钢中总氧量 ［TO］是衡量钢洁净度的重要标识,对于不同的钢种,其控制要求也不尽相同。在脱氧精炼过程中,存在着脱氧元素-钢中溶解氧、钢-渣、钢液-夹杂物、钢液-耐火材料、渣-耐火材料的反应与平衡,对钢中夹杂物的数量、组成和形态具有重要影响。通过热力学计算,比较了不同脱氧剂的脱氧能力,并介绍了典型特殊钢种（轴承钢、弹簧钢、帘线钢、电工钢、易切削钢等）精炼过程中的脱氧及夹杂物控制,分析和讨论了不同脱氧元素与钢液、熔渣以及耐火材料之间的相互作用机制。     

经济型耐腐蚀钢中氧作用的研究

为了冶炼不同氧含量的碳素船体钢,通过机械性能试验和周浸试验研究了钢中氧含量对钢材腐蚀性能和机械性能的影响。结果表明,在连铸生产许可的氧范围内,随着钢水脱氧程度的减弱,钢中氧质量分数增加,钢材的平均腐蚀率略有下降,而耐点蚀性能有较明显增强,变化曲线的高氧端比低氧端平均点蚀深度下降约22.7%。弱脱氧钢的机械性能符合规范要求,可达到D级钢水平。分析认为,氧提高钢材耐蚀性的原因主要是固溶氧可提高铁的热力学稳定性,提高了蚀孔内铁的腐蚀电位,降低了蚀坑扩展速度。氧作为耐蚀元素应用可以显著降低耐蚀钢的成本,提高经济性。      

Thermodynamics of the oxygen solutions in iron-nickel melts

The oxygen solutions in Fe-Ni melts containing chromium, manganese, vanadium, carbon, silicon, titanium, or aluminum are studied thermodynamically. The equilibrium constants of the deoxidation of the melts by these elements are determined, and the activity coefficients for infinite dilution and the interaction parameters in alloys of various compositions are found. The oxygen solubilities in the alloys are calculated as a function of the nickel and deoxidizer contents. The deoxidizer contents at the minima in the oxygen solubility curves for the melts are determined, and the corresponding minimum oxygen concentrations are calculated. As the nickel content in the system increases, the deoxidizing capacities of chromium, manganese, and silicon are shown to increase substantially, and the deoxidizing capacity of carbon increases most strongly. As the nickel content in the melt increases, the deoxidizing capacities of vanadium and titanium first decrease insignificantly and then increase substantially. As the nickel content in the melt increases to 50%, the deoxidizing capacity of aluminum first decreases and then increases; in pure nickel, it is identical to that in pure iron.     

RH炉脱硫过程特征热力学分析

在硅钢RH炉精炼过程脱硫实践中发现,RH精炼炉中投入一定量脱硫剂,可以起到脱硫作用。但在[Al]、[Si]含量较高的钢种,没有投入脱硫剂也有脱硫效果。另外,RH炉脱氧前也有一定的脱硫效果,RH炉结束的硫含量一般都要比中间包内硫含量要高。通过热力学理论计算发现,RH炉精炼过程脱硫可以分为两个阶段：第一阶段是钢水脱氧前,钢水中[C]和[S]反应生成CS气体,有较弱的脱硫效果;第二阶段是脱氧后脱硫阶段,钢 渣扩散脱硫、钢水中[Si]和[S]反应生成SiS气体和钢水中[S]、[Al]、[Si]和[Ca]相互作用最终生成CaS。钢水中较高的[Al]和[Si]含量对第二阶段脱硫效果有较大的正向影响。进一步的,转炉结束前CS、SiS气体的生成使得铁水[C]元素有一定的脱硫作用。CS气体在转炉持续供氧过程和铁水裸露在空气中时,被氧气氧化生成SO2气体。CaO-CaF2系RH炉用脱硫剂中的CO2组分能够氧化钢水中的[Al]、[Si]等合金元素,同时造成钢水增碳。     

Control and Engineering of Non‐metallic Inclusions belonging to xSiO2‐yCaO‐zAl2O3 System in Ca‐treated Al‐killed and Al‐Si‐killed Steel

A model based on the fundamental principles of thermodynamics has been applied to forecast and control the precipitation of non‐metallic inclusions in Ca‐treated Al‐killed or Al‐Si‐killed steels. The engineering of the non‐metallic inclusions takes place during the period just after the tapping from the electric arc furnace until the beginning of the casting period. The construction of the model and its validation have been accomplished through a precise monitoring of the treatment of several steel grades characterized by different oxygen contents after tapping. The oxygen killing of the steel melt with an oxygen content between 750‐1200 ppm is performed by the addition of Si and Al, which produces the formation of pure Al₂O₃ but not always the formation of pure SiO₂. This is a fundamental hypothesis of the model confirmed by experimental observations. The other fundamental aspect is related to the determination of the oxygen activity in the steel bath, which is defined from experimental measurements by an electrochemical concentration cell and through the computation of the equilibrium between the steel bath and the ladle slag. The comparison between the experimental data and the non‐metallic evolution forecast by the model on the basis of the minimization of the oxygen potentials has shown very interesting performances, which makes the model a suitable and very stable tool for industrial application.     

采用石油液化气进行钢液脱氧

在实验室利用石油液化气对钢中氧进行去除.研究结果表明:利用石油液化气对钢液脱氧是可行的,配合VD真空冶炼,可用于生产高碳、高质量洁净钢.钢液脱氧时,通入氩气和液化气两者的混合气体的脱氧效果优于单纯通入单一气体,钢中氧含量下降更明显,碳含量增加幅度更低.混合气体对钢液脱氧操作8 min后,钢中脱氧减慢,氧含量下降不明显.钢液脱氧的起始阶段,钢中碳含量增加较为缓慢,当钢中氧含量降低到一定水平后,钢中碳含量迅速增加.通入氩气,加强了钢液搅拌,在一定程度上抑制钢中氢含量的增加速度,促进了钢中氢的去除.      

镁合金对钢液脱氧脱硫的作用

用镁合金脱氧剂在MgO质感应炉上对低碳钢进行了脱氧行为的研究.实验主要选取AlMg、SiCaBaMg、SiCaBaAlMg镁系合金与Al进行脱氧对比,考察了脱氧后钢水的T[O]、[S]以及夹杂物的变化情况.与Al相比,SiCaBaAlMg包芯线、AlMg 1#脱氧效果较明显,镁合金在脱氧的同时具有稳定的脱硫能力,并且脱氧后夹杂物的粒径有不同程度减小.     

Oxygen Solubility in Fe–Co Melts Containing Carbon

In thermodynamic analysis of solutions of oxygen in Fe–Co melts containing carbon, the equilibrium constants of reactions between carbon and oxygen are determined, as well as the activity coefficients at infinite dilution and the interaction parameters in melts of different composition at 1873 K. The dependence of oxygen solubility in such melts on the cobalt and carbon content is calculated. In iron–cobalt melts, carbon has high oxygen affinity. The deoxidizing ability of carbon increase significantly with increase in cobalt content in the melt. In pure cobalt, it is more than an order of magnitude greater than in pure iron. Deoxidation by carbon produces gaseous oxides: carbon monoxide (CO) and dioxide (CO₂). The reaction of carbon and oxygen dissolved in the melt and hence the deoxidizing ability of carbon depend on the total gas pressure above the melt. Decrease in gas pressure significantly improves the reducing properties of carbon. The minimum oxygen concentration for alloys of the same composition is reduced by practically an order of magnitude with tenfold decrease in the total gas pressure. The gas composition above Fe–Co melts and the equilibrium carbon and oxygen concentrations in the melt are calculated with total gas pressures of 1.0, 0.1, and 0.01 atm. The optimal oxygen concentration (1–10 ppm) in Fe–Co melts is reached at carbon concentrations between 0.01 and 1% depending on the total gas pressure (0.01–1 atm). The solubility of oxygen in iron–cobalt melts containing carbon passes through a minimum, which is shifted to lower carbon content with increase in the melt’s cobalt content. Further additions of carbon increase the oxygen concentrations in the melt. With increase in cobalt content, this increase will be sharper.     

Thermodynamic Properties of Inclusions Formed Aluminum-Titanium Deoxidation of Molten Steel

Titanium alloyed steel has been widely used as automobile sheet steels, thick plate steels, and also stainless steels to improve the mechanical and chemical properties of many grade steels. Since Ti has strong affinity with oxygen, Ti is normally alloyed after Al deoxidation to keep the high yield of Ti. Therefore, Al-Ti deoxidation is one of the common and important secondary refining processes. Although the chemical stability diagram for this system has been reported by many researchers, these diagrams are inconsistent significantly each other. In the present study, the stability region of Al2TiO5 oxide was measured by equilibrating Fe-Al-Ti alloy and Al2TiO5 pellet in Al2O3 crucible at 1873 K. However, inclusions in metal after equilibration were Ti-containing Al2O3 or Al-containing TiOx. The precise phase diagrams and related thermodynamic data for the Al2O3-TiOx-FeO system should be determined.